Communicating system for power-transmission lines



April 28, 1931. M. SINDEBAND ET AL 1,303,149

COMMUNICATING SYSTEM FOR PCWER TRANSMISSION LINES Original Filed Jan. 28; 1920 I I /6 z 0 W 5 a a g E 6:

O 8 40 E E7;

9 S v ,i7im Z2 I/ 20 Invent ors:

Maurwce L. Sindeband George N. Tidd Joseph Milnor Their Attorney Patented Apr. 28, 1931 rare OFFICE MAURICE L. SINDEBAND, YORK, N. Y., GEORGE N. TIDD, ELIZABETH, AND

JOSEPH W. MILNOR, OF MAPLEWOOD, NEW JERSEY, 'ASSIG-NORS TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK COMMUNICATING SYSTEM FOR POWER-TRANSMISSION LINES Griginal application filed January 28, 1920, serial No.:354,602. I'aten-t No. 1,724,112, dated August 13, 18-29. Divided and this application filed November 25, 1927'. Serial No.'235,430.

The present invention relates to communicating'systeins for power transmission l nes and more particularly to a system for telephoning over a line employed to transmit power. Such a system is disclosed in our copending application Serial No. 354,602, filed January 28, 1920, (which issued as Patent 1,72%,112, August 13, 1929), of which the Jresent application is a division.

rllternating transmission lines have long since been employed to transmit power to points distantfrom the source of power.' In order properly to operate these systems and to render them effective, it is desirable that some form of reliable, private communicating system, such as the telephone, be provided between the power supply station and the consuming station or stations. Heretofore it has been suggested that telephone communication may be transmitted to some extent over power lines by superimposing voice frequency currents upon the power frequency currents of the transmission line, as disclosed in the patent to Bedell No. 715,587. As indicated in that patent, however, the transmission of voice frequency over power transformers is unsatisfactory owing to various causes, among which maybe mentioned the inability to completely remove harmonics of the power system from a receiver without removing voice frequency currents as well. Such a system, in which a receiver is not re sponsive to voice frequencies only, is obviously of little practical value.

The present applicants have found that if modulated frequencies, upward of 5000 cycles, be superimposed on a power line and proper- 1y tuned circuits employed, such modulated high frequency currents may be transmitted over ordinary power transformers to receivers tuned to the frequency of the transmitted signal and that in the received signal will be unaffected by the power frequency current.

The novel features which are believed to be characteristic of the present invention are et forth with particularly in the appended claims. The invention itself, however, will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which the single figure shows adiagrammatic view embodying the features of our invention. V

lVhile the invention is applicable to an alternating current transmission line of any number of phases, we have shown it applied to a three-phase system. In the figure the power is adapted to be supplied to the transmission line through conductors 1 supplied by a suitable generator Qand a step-up transformer 3. The secondary winding of the latter is connected to the three-wire transmission line indicated at 1, 5 and 6. The other end of the transmission line is shown connected to the primary winding of a stepdown transformer 7, the secondary winding of which is connected to lines 8 which are connected to the load. The system thus far described is one commercially employed for high tension transmission. We employ the power conveying line as the signaling line by suitably coupling transmitting means at at least one station and receiving means at the other station, or, if desired, a receiver and transmitter may be employed at both stations.

At station 9 we have shown agenerator 10 of alternating current having a frequency different from the frequency of the power. current supplied to the lines 4, 5 and 6. For example, if the power frequency is 60 cycles per second the frequency of generator 10 is at least 5000 cycles or higher. The generator 10 is shown connected to a microphone or transmitter 11 which is adapted to modulate the high frequency current supplied to the hightension side of transformer 3 by generator 10. The latter is connected to one phase of the lines 1 by means of a current transformer of which one winding is designated 12. V V

In order substantially to prevent the power current from reacting on the transmitting circuit, the means'shown at 13, 14 may be employed. It will be seen that inductance 18 andcapacity 14 are. connected in parallel. across the winding 12and these impedances are designed or adjusted for parallel resonance, for example, to be anti-resonant at paratively low. This means that so far as the passage of signaling current in the trans nntting circuit is concerned the set .13, 14 is substantially of no effect. On the other hand, Y

practically all of the lower frequency; current introduced into the local receiving circuit by the wnidmg 12, passes through the elements 13, 1 1 by virtue of the compara-- tively low impedance of the latter. power frequency. V

The receiving means at station 15 is shown as comprising a current transformer 16, having windings connected to the low tension side of transformer 7 and to two phases of the lines 8, an inductance 17 and capacity 18 in all respects similar to the corresponding elements 12, 13 and 1 1 at the station 9. A telephone receiver 19 is connected in series witlrwinding 16 and a crystal detector or other suitable rectifier 16. An inductance 20 and capacity 21 designed for parallel resonance at the frequency of the generator 10 may be shunted across the receiver 19 for thepurpose of shunting out any power frequency current which may pass the antiresonant set 17 18.

The impedances 22, 23 are preferably so designed or adjusted that the receiving circuit containing the receiver 19 will be tuned to or resonant at the frequency-of generator '10 whereby a maximum amount of signaling current will flow through 1'eceiver19. linpedai'lces 22, 23 are also preferably designed or adjusted for series resonance at the signaling frequency. With such design the combined impedance 22, 23 will materially restrict the flow of any power frequency current which may pass the set 17, 18. i

In operation, it is assumed that the lines 4, 5 and 6 arecarrying currentat cycles. If the operator at station 9 spel into the device '11 thus modulating the high frequency current supplied by generator 10 the eound vibrations will be'reproduced at 19 in a manner which will be apparent to those skilled in the art. Since the receiving-circuit at station 15 is tuned to the frequency of the generator 10, the operator at 15 will hear the transmitted message by means of the receiver 19. Due to the shunts 17, 18 and 20, 21 as well as the impedance offered to the power current by the elements 22, 23 the receiver 19 will be free from any noise which would otherwise be caused by th power current. Signaling from station 15 to station 9 may be accomplished if desired i a similar manner. 3

at the winding of the source 2and the secondary of the current transformer 12. As a result of thisconnectmn a high frequency carrier electrom'otive force 1s produced between the terminals of each of the primary windings.

mentioned. On the secondary side of transformer 3, signaling current circuits may be traced in which the secondary windings of the transformer, the conductors 1, 5 and 6 and the primary windingsof transformer 7 are connected in series relation. Signaling currents transmitted through such a circuit are in turn impressed upon a circuit associated with the receiver which includes one of the secondary windings of transformer 7 the two conductors with which current transformers 16 are associated and any load devices which may be connected between these conductors.

t will be appreciated from the above description that we have provided a communicating system in which the power conveying conductors alone are employedto convey the signaling current without any substantial interference with the power transmission. No line wires, other than the power lines, are required so that the installation as well as maintenance costs are minimum. Furthermore, by virtue of the sets 13, 1 1; 17, 18; 20, 21 and 22, 23 which are designed or'adjusted for parallel orantiresonance at the signaling frequency employed there is practically no noise caused in the receiving instrument by the low frequency power current.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A combined power and telephone system comprising in combination'a source of alternating current power having a low frequency, a transformer, a transmission line, said transformer having a winding connected across said source of alternating current power and a second winding connected across said transmission line means for producing a high frequency carrier electromo'tive force across one of said windings, said electrometiveforce having afrequency materiallyhigher than the usual voice frequencies, means for modulating said carrier electromotive force with currents of voice frequency, a carrier current receiver which is responsive to electromotive forces produced across the other of said windings of said transformer and adapted-toreproduce said voice frequencies and means for excluding power currents from said receiver.

2. A combined power and signal system, comprising in combination a source of alternatlng current power having a low frequency, a transformer having a pair of wind-. lngs, a transmission line, the terminals of one of said windings being connected to opposite sides of said source and the terminals of the other of said windings being connected across said transmission line, means for producing a carrier frequency electromotive force between the terminals of one of said windings, said electromotive force having a frequency of at least 5000 cycles, whereby said carrier frequency electromotive force appears between the terminals of said other winding, means for modulating said electromotive force in accordance with desired signals, a carrier current receiver connected to respond to said carrier frequency electromotive force appearing between the terminals of said other winding, said carrier current receiver being adapted to reproduce said si nals, and means for excluding currents of the power frequency fromsaid receiver.

3..A combined power and communication system comprising in combination a source of alternating current power of low frequency, a power transformer having primary and secondary windings, the primary winding being connected to said power source and the secondary winding being connected to a power transmission line, means for supplying a signaling current having a frequency materially higher than the usual voice frequencies to one of said transformer windings in such a way that the winding to which the signaling current is supplied is connected in series in the signaling current circuit, means for modulating said signaling current at an audio frequency, and a receiver coupled to a circuit supplied with power current from the secondary winding of said transformer in such a way as to have impressed thereon signaling current transmitted through a circuit in which the secondary winding of the transformer is connected in series, said receiver being responsive to the signaling frequency only and adapted to reproduce current of the modulating frequency.

4. A combined power and communication system comprising in combination a source of alternating current power of low frequency, a transformer having primary and secondary windings, the primary winding being connected to said power source, and the secondary winding being connected to a power transmission line, a source of signaling current having a frequency materially higher than the usual voice frequencies, means for inductively coupling said source of signaling current to a signaling current cir cuit which includes one of said windings in series therein, means for modulating said signaling current, a signal currentreceiver and means for impressing upon the receiver signaling currents WlllCh are supplied thereto through a circuit in which said other windcurrent power of low frequency, a trans-l former having primary and secondary w1nd- I ings, the primary winding being connected to said power source and the secondary wmdlng being connected to a transmission line, means for supplylng modulated high frequency signaling currents having a frequency of at least 5000 cycles to a signaling current cirf cuit which includes one of said transformer windings in series, a signal current receiver,

and means for impressing upon said receiver signaling currents supplied through a circuit which includes the other transformer winding in series therein, said receiver being responsive to the signaling frequency only, and being adapted to reproduce currents cor responding to the modulations of the signaling current. i

6. 'A' combined power and communication system comprising in combination a source of alternating current power of low frequency, a transformer having primary and secondary windings, one of said windings being connected to said source and the other'of said windings being connected to a power trans mission line, means for supplying modulated signaling currents having a frequency higher than the usual voice frequencies to a circuit which includes one ofsaid windings in series therein, a signal receiver, and means I for supply signaling currents to said receiver through a circuit which includes the other of said windings in series therein, said receiverbeing responsive to the signaling frequency onl andbeing adapted to reproduce currents corresponding to the modulations of the signaling currents.

7. A combined power and communication system comprising a source of alternating current of low frequency, a transformer having prlmary and secondary windings, one

of said windings being connected to the source of power and the other of said windings being connected to a transmission line, a transmitter arranged to supply modulated signaling current having a frequency above the range of the usual voice frequencies to a circuit which includes one of said windings in series therein, a signal receiver, means for supplying signaling currents to said receiver through acircuit which includes the other of said windings in series therein, means for excluding power frequency currents from said transmitter, and means for excluding currents from said receiver having a he quency different from the signal frequency. 8. A combined power and communication iii system comprising a source of multiphase alternating current power of low frequency, a transformer having sets of multiphase primary and secondary windings, the primary windings being connected to said source and the secondary windings being connected to a power transmission line; means for supplying toat least two of one set of said windings modulated signaling currents having a frequency materially higher than the power frequency, a signal receiver; and means for supplying to said receiver signaling current transmitted through at least two of the other sets of windings the connections being so arranged that the windings to which signalmg currents are su-pphed'are connected 111 series with the source of signaling currents and in parallel with one another, and the windings which serve to transmit signaling currents to the-receiver are connected in series relation in a signaling current circuit with which the receiver is associated.

In witness whereof, we have hereunto respectively set our hands-the 19th day of Noveniber, 1927, the 15th day of November, 1927,

and the 17th'day of'November, 1927. V

MAURICE L. ,SINDEBAND. GEORGE N. TIDDI JOSEPH MILNOR. 

